A device of the aforementioned kind is known, for example, from DE 195 27 138 C1. In the apparatus described there, the displacement head is connected at its forward end with a splitting wedge serving to break up or destroy an old and to be replaced supply conductor laid in the earth. One such splitting wedge is especially necessary if the replaced pipe is a cast pipe. These cast pipes have every four to six meters a very thick walled socket that has to be destroyed.
If the pipe to be replaced is made of cement or stone materials, such a splitting wedge is not absolutely necessary.
The displacement head, whose forward diameter is smaller than the inner diameter of the pipe to be replaced and whose rear diameter is larger than the outer diameter of the new pipe to be drawn in serves so that the broken pieces of the pipe to be replaced are pressed outwardly into the earth and so that the earth bore is so widened that the new pipe can be drawn into it.
The pipe to be drawn in is inserted at its forward end into the cylindrical shaft and in the known solution is secured by the help of bolts, which are threaded into threaded bores in the rear portion of the cylindrical shaft and are received in radial bores which pass through the pipe to be drawn in.
A disadvantage of this solution is that the cylindrical shaft is not smooth on its outside. To avoid the heads of the screwed bolts from being torn off, deflecting elements are welded onto the outer circumferential surface of the cylindrical shaft. Therefore considerable forces appear at these points when the apparatus is driven through the earth. In extreme cases, the displacement head can be torn from the cylindrical shaft.
It is further known that the new pipe can be drawn in with the help of a cable and a cable gripping apparatus which is fastened to the rear end of the new pipe and which is connected with the cable. This solution has the disadvantage that the cable stretches heavily upon being loaded in tension. In the case of a pipe to be drawn in of 100 m length, this can lead to the tension cable being elongated by about 1 m. Thereupon, the pipe to be drawn in can move out of the cylindrical shaft of the apparatus and can become jammed in the earth bore.
The invention has as its object the provision of an apparatus of the aforementioned kind with which the pipe to be drawn in can be connected with the cylindrical shaft of the apparatus in a simple way whereby the outer circumferential surface of the cylindrical shaft remains entirely smooth.